The thermoelectric conversion element is applied to thermoelectric conversion power generation or thermoelectric conversion cooling. For example, for the thermoelectric conversion power generation, a temperature difference is applied to the thermoelectric conversion element to generate thermoelectromotive force, and then the thermoelectromotive force is used to convert thermal energy into electric energy.
Energy conversion efficiency of the thermoelectric conversion element depends on ZT value that is a performance index of thermoelectric conversion material. ZT value is determined by Seebeck coefficient, electric conductivity and thermal conductivity. In more detail, ZT value is in proportion to electric conductivity and square of Seebeck coefficient and in reverse proportion to thermal conductivity. Thus, in order to enhance the energy conversion efficiency of a thermoelectric conversion element, it is required to develop thermoelectric conversion materials with high Seebeck coefficient, high electric conductivity or low thermal conductivity.